In response to a United States Environmental Protection Agency requirement, EMD has developed a family of kits including components to be substituted for the corresponding components originally provided with various types of 645 model engines in order to meet a requirement for reduced emission of nitrogen oxides (NOx). It is known that NOx emissions can be reduced by retarding fuel injection timing. However, this generally leads to an increase in smoke, CO and particulate emissions. It is also known that reducing engine airbox temperature contributes to lower NOx emissions. Previously, the 645 model engines had used two pass parallel flow aftercoolers. However, improved four pass counterflow aftercoolers were known to provide reduced airbox temperatures.